Automated fiber placement is a process that is widely used for fabricating composite structures using pre-impregnated composite materials, such as carbon fiber, fiber glass and Kevlar. The materials, for use in automated fiber placement, typically take the form of a strip or yarn of composite material impregnated with a resin.
During automated fiber placement, groups of tows or tapes are deposited on a mold or tool by an automated fiber placement machine, to form a composite structure. The fiber placement machine includes a fiber placement head which has provisions for simultaneously handling groups of, for example, 12, 24, or 32 tows, which are positioned parallel to one another by the fiber placement head to form a substantially contiguous band of pre-impregnated composite material.
During the fiber placement process, it is sometimes necessary to cut and stop the feed of individual tows, thus removing them from the band of material, in order to reduce the width of the band so that it may be placed onto the surface of the mold or tool in a manner that precludes having excessive gaps between successive bands of material, or having the edges of successive bands of material overlap one another. In similar fashion, it is often desirable to add tows to the band in order to increase its width, at various stages of the automated fiber placement process, in order to facilitate manufacture of the composite structure. The process of removing or adding tows is commonly referred to “cut and add” (cut/add).
Automated fiber placement machines are capable of depositing material onto a tool surface at high feed-rates, of, for example, 1200 inches/minute or higher. For maximizing productivity, it is desirable to operate an automated fiber placement machine at such high feed-rates throughout the fabrication of a composite structure. It is highly desirable, therefore, that automated fiber placement machines be capable of modifying the width of the band of material being applied without stopping, or slowing down, the machine to cut or add tows to the material band. In the vernacular of the automated fiber placement industry, it is highly desirable that automated fiber placement machines be capable of cutting or adding tows “on-the-fly.”
In order to cut or add tows to the material band on-the-fly, the cut/add process must take place in real time. The components of the automated fiber placement machine which perform and control the cut/add process are incapable of instantaneously cutting or adding a tow to the band of material, due to inherent and unavoidable lag times or other latencies in the operation of mechanical, hydraulic, pneumatic, or electrical actuation and control components of the automated fiber placement machine. These unavoidable and inherent latencies result in the end of a cut or added tow often being positioned well outside of the tolerances required for constructing the composite structure where on-the-fly cut/add is attempted at full operating speed using prior fiber placement machines.
The problems described above, with regard to cut/add operations, are also encountered in other operations performed at high-speed on-the-fly during fabrication of a composite structure, such as changing tension, temperature, or pressure applied on a tow or the material band during automated fiber placement.
What is needed, therefore, is an improved method and apparatus for performing high-speed events on-the-fly during fabrication of a composite structure by automated fiber placement.